This invention relates generally to improvements in respiratory face masks of the type worn over a person's nose and mouth to filter inhaled and exhaled air. More particularly, this invention relates to an improved face mask designed for substantially minimizing re-inhalation of exhaled gases.
A wide variety of respiratory face mask constructions are known in the art. In general terms, such face masks comprise a finely porous filter material adapted to be worn over a person's nose and mouth to filter inhaled and exhaled air, particularly for purposes of removing airborne particulate and contaminants. Available face masks are constructed from a variety of controlled porosity filter materials including, for example, paper based and/or plastic fiber materials, foam materials and the like. In some designs, the filter material is provided in a contoured, generally shell-shaped configuration for mounting over the person's nose and mouth by means of an elastic strap. In another form, the filter material is wrapped over the nose and mouth in a manner similar to a scarf.
Respiratory face masks of the general type described above are used extensively in a wide variety of different applications. For example, face masks have been used for many years by medical and dental personnel to minimize or eliminate transfer of infectious disease from or to the patient during treatment. These types of face masks are also used in a wide range of industrial applications to prevent inhalation of harmful substances such as paint particles and other particulate contaminants. In recent years, face masks have been used with increasing frequency by individuals suffering from respiratory allergies and/or other respiratory disfunction to reduce inhalation of plant pollens.
In the past, a preferred face mask construction has generally required a close anatomical fit between the filter material and the facial contours of the person's nose and mouth to minimize leakage around the edges of the mask during inhalation and exhalation. As a result, a widely used prior art face mask has typically provided a close-fitting construction as exemplified by a disposable contoured mask of the type marketed by Minnesota Mining and Manufacturing Company, of St. Paul, Minn., under the model designation 1942F. Unfortunately, in close-fitting masks of this type, the small pore size and resultant reduced porosity of the filter material tends to both reflect the exhaled gas onto the face of the wearer, and reduce the velocity of the exhaled gases sufficiently that the interior of the face mask is often enveloped by the exhaled gas, which includes a high proportion of relatively warm carbon dioxide and water vapor under pressure. This warm moisture saturated air is thereupon held in close proximity to the facial skin of the mask wearer, and is directly re-inhaled through the nose and mouth. As a result, a high proportion of the exhaled gasses are simply re-inhaled, resulting in significant impairment of breathing comfort. In addition, the high content of water vapor present in the exhaled gas also results in repeated and continued fogging of any protective or corrective eyeglasses that may be worn, thereby effectively obscuring vision.
The present invention provides a significant improvement in the construction of a simple respiratory face mask, particularly with respect to a relatively simple yet highly effective face mask construction which substantially reduces re-inhalation of exhaled gases, and further which relieves the wearer of the discomfort of warm moist exhaled air trapped against the facial skin.